Joint effects of excessive fluoride and iodine on thyroid function among children in Tianjin

ObjectiveTo investigate the joint effects of excessive fluoride and iodine on thyroid function among children in Tianjin.MethodsAccording to the concentration of fluoride and iodine in drinking water,four small towns in two counties of Tianjin were classified into three groups of high fluoride and iodine,high fluride,and control.Children aged 8-10 years in the four towns were chosen.The morning urine was collected and venous blood was taken from the children before breakfast.The concentrations of urinary fluoride,urinary iodine,triiodothyronine(T₃),thynoxine(T₄),thyroid stimulating hormone(TSH),free T₃(FT₃),and free T₄(FT₄) in the serum were detected.Maleicdialdehyde(MDA),superoxide dismutase(SOD),and reactive oxygen species(ROS) were also measured.ResultsThe concentration of iodine in the urine of the children from high fluoride and iodine,high fluoride,and control group were 721.7,788.3,and 293.5 μg/L and those of fluoride were 2.48,2.70,and 1.59 mg/L.Significant increases in urinary fluoride and iodine were observed in the children of high fluoride and iodine,and high fluoride groups compared to the control group (F=24.1,P=0.000;F=11.0,P=0.000).The concentrations of T₄ in the serum of the children from high fluoride and iodine,high fluoride,and control group were 95.0,86.2,and 89.2 ng/L.Thyroid hormone T₄ in the children of high fluoride and iodine group was higher than that of high fluoride group (F=4.0,P=0.021),but there were no significant differences in other thyroid hormone (T₃,FT₃,FT₄ and TSH) among the three groups.The concentration of ROS in the serum of children from high fluoride and iodine,high fluoride, and control group were 89.95± 63.85,76.65±125.45,and 72.83± 13.70 U/ mL,and those of the activity of SOD were 2.14±5.20,2.22±2.50,and 0.79±0.90.ROS in the children of high fluoride and iodine group was higher than that in high fluoride group (χ²=14.9,P=0.001),but the activity of SOD demonstrated an inverse trend(χ²=20.9,P=0.000).The difference in MDA was not statistically significant among the groups (χ²=0.9,P=0.626).The content of urinary iodine had a positive correlation with ROS(r=0.226,P=0.026),and an inverse correlation of urinary iodine with SOD was identified(r=-0.264,P=0.009).ConclusionThe exposure of high fluoride combination with iodine has a definite impact on children's thyroid function,but has no significant impact on other thyroid hormone except T₄.Oxidative stress indexes such as ROS and SOD are closely related to urinary iodine and fluoride.